1. Field of the Invention
The present invention relates to a wired circuit board and a producing method thereof and, more particularly, to a wired circuit board such as a suspension board with circuit and a producing method thereof.
2. Description of the Related Art
There has been conventionally known a suspension board with circuit including a metal supporting board made of stainless steel, an insulating layer made of a polyimide resin formed thereon, and a conductive pattern made of copper formed thereon.
In recent years, in terms of higher data density, an increase in the frequency of a signal has been required in such a suspension board with circuit. However, when the frequency of the signal is increased, a transmission loss increases undesirably in the conductive pattern.
To reduce such a transmission loss, there has been proposed a transmission line which includes, e.g., a lower insulating layer formed on a stainless steel layer, a lower conductor formed on the lower insulating layer, an upper insulating layer formed on the lower conductor, and conductors composed of a record-side line and a reproduction-side line which are formed on the upper insulating layer (see, e.g., Japanese Unexamined Patent Publication No. 2005-11387).